1. Technical Field
The present invention relates to compositions and processes for the chemical mechanical planarization of surfaces in the fabrication of integrated circuits, and more particularly, to the use of ozone as an oxidizing agent in chemical mechanical planarization.
2. Description of Related Art
Chemical-mechanical planarization (CMP) is a process employed to remove various materials from wafer surfaces during the manufacture of integrated circuits, creating thereby a substantially planar surface that facilitates accurate patterning and deposition of subsequent layers. Typical CMP processes use a polishing pad rotating in contact with the wafer to be planarized with the introduction of a suitable CMP reagent between the wafer and polishing pad to facilitate material removal and planarization. CMP reagents typically include an abrasive slurry containing, among other components, abrasive particles and various oxidizing agents. Abrasive particles used for CMP include alumina, silica, spinel, ceria, zirconia, among others.
The areas of applicability of CMP processes have expanded to cover a large variety of materials, including metals. This expansion of applicability has stimulated a continuous search for new oxidizers that will make CMP processes of metal more effective. Oxidizers such as hydrogen peroxide, potassium ferricyanide, periodic acid, hydroxylamine and its salts, and other such oxidizers have resulted from this continuous search and are currently being employed in CMP processes of metal. However, these oxidizers have several drawbacks including, inter alia, they create waste streams such as ionic waste streams that must be treated and removed from CMP process areas. Additionally, these waste streams may also include metal oxides from the wafer surfaces themselves. Such waste streams are rather complex and are quiet difficult to treat and dispose of effectively. For the foregoing reasons, among others, there is a need for an oxidizer that will make CMP processes of metal more effective and reduce challenges associated with treating the typical ionic and complex waste streams of conventional CMP and their associated hazards to the environment.
The present invention provides chemical compositions and processes that increase the effectiveness of CMP processes (typically CMP of metals) and/or ameliorate the challenges of treating and disposing of present day ionic and complex waste streams in an environmentally friendly manner by making use of ozone (O3) in aqueous and/or gaseous form. For example, the chemical compositions and processes pursuant to the present invention are particularly advantageous for CMP processes of tungsten, copper, silver, gold, platinum, iridium, ruthenium, and aluminum metals as well as for CMP processes of organic materials having a low dielectric constant (xe2x80x9clow kxe2x80x9d).
Ozone has been used as a component of cleaning solutions used for contamination control and cleaning separate from the CMP process. For example, see Stanley Wolf and Richard N. Tauber, SILICON PROCESSING FOR THE VLSI ERA, Volume 1: Process Technology, 2nd Ed. (Lattice Press, 2000), pp.131-133. Ozone cleaning of wafer surfaces following CMP is described, for example, by E. K. Greiger et. al., U.S. Pat. No. 6,100,198. Ozone has also been used as an oxidizer in the formation of structures integral to the integrated circuit. For example, ozone-enhanced local oxidation of silicon is used in forming a field isolation structure in the work of Thakur et. al. (U.S. Pat. Nos. 5,672,539 and 6,072,226). Ozone-rich TEOS layers (tetraethoxysilane layers) have been used in the formation of dielectric layers on integrated circuits in the work of Chen and Tu (U.S. Pat. No. 5,869,394) and Jang et. al. (U.S. Pat. No. 6,143,673).
However, in contrast to the prior art, the present invention makes use of ozone as a reagent in the practice of CMP. Ozone is employed in the form of a gas delivered directly to the surface to be planarized, and/or used in the form of an ozone-containing aqueous solution, optionally used in combination with abrasive particles, in combination with other CMP reagents, or used in other embodiments described herein and/or obvious to those having ordinary skills in the art.
The present invention relates to the use of ozone (O3) as a reagent in chemical mechanical planarization. Ozone can be delivered to the surface to be planarized in several forms, including in an aqueous solution or as a gas. An aqueous solution containing ozone may optionally contain abrasive particles and/or additional CMP reagents co-dissolved with the ozone. Co-reagents useful in CMP in cooperation with ozone include carbonate and bicarbonate anions, and organic acids such as formic, oxalic, acetic and glycol. Ozone can be delivered directly to the surface to be planarized in the form of a gas. Combinations of the foregoing ozone-containing reagents can be employed in CMP, optionally in cooperation with other non-ozone-containing CMP reagents, within the scope of the present invention.
Ozone (O3) is typically formed in an ozone generator by passing oxygen through an energy field, typically a plasma or ion field, forming ozone in situ. In some embodiments of the present invention, it is convenient to generate the ozone and/or the ozone-containing reagent (or reagents) on-site as needed and proximate to the CMP apparatus where the ozone-containing reagent(s) will be consumed. Some embodiments of the present invention make use of ozone dissolved in water (preferably DI water) to form an aqueous solution. Typically the concentrations of ozone in DI water will be in the range from approximately 1 part-permillion (xe2x80x9cppmxe2x80x9d) up to saturation, possibly exceeding 20 ppm. Such an aqueous solution can be used directly for CMP, dispensing the solution between a wafer surface and a polishing pad to affect planarization.
Other embodiments of the present invention make use of ozone dissolved in water along with additional abrasive and/or reactive chemicals. Abrasives that may be added include alumina, silica, spinel, ceria, zirconia. Other reagents that may be added include carbonate and bicarbonate anions, oxalic acid, formic acid, acetic acid and glycol acids.
Ozone gas may be directly impinge on the surface to be planarized pursuant to other embodiments of the present invention.
The compositions of the present invention can be used for CMP of platinum and other materials that are difficult to planarize with conventional oxidizers. Other metals include ruthenium, iridium, gold and aluminum. The compositions of the present invention can also be employed to coact with silicon such that it can be polished to better surface finishes. Material removal can be facilitated pursuant to the present invention by the inclusion of ammonium salts, including ammonium chlorides, ammonium nitrate and particularly ammonium carbonates.
Ozone compositions pursuant to the present invention break down typical organic polymers, rubber or other low k materials, thereby directly polishing organic low k dielectric films.
The compositions of the present invention may be employed for polishing hard disk and micro electrical mechanical structures (MEMS) including films containing NiP, Cr, Al, SiO2, Si or Al metal.